Problem: Evaluate the following expression when $b = 1$ and $a = 9$. $8$ $b$ $ + 7$ $a$ $ - 9$
Explanation: Substitute $1$ for ${b}$ and $9$ for ${a}$ $ = 8{(1)} + 7{(9)} - 9 $ $ = 8 + 63 - 9 $ $ = 62$